1. Field of the Invention
The present invention relates to a semiconductor IC, particularly to a temperature sensing circuit having a temperature range control unit.
2. Description of the Related Art
With new electronic products persistently emerging, more and more functions are integrated into a single product. For example, the digital camera and MP3 player are being integrated into a mobile phone or many multimedia devices are being integrated into a notebook computer. As a result, manufacturers need to incorporate more chips into a single electronic product to satisfy such functional integration. In addition, with the increasing of CPU clock frequency at the same time, more heat is generated within the electronic product. However, overheating of any electronic product may result in data loss, system instability, or even chip burnout. An external temperature sensing element not only increases the manufacture cost, it also can not measure the temperature of the chip precisely. Therefore, the common solution is to implement a temperature sensing circuit within IC, which has the advantages of small size, fast response, high accuracy, low power consumption and easy software control.
The temperature sensing circuit usually allows the user to preset a temperature range. Once the temperature range is exceeded, a procedure is executed to lower the temperature automatically, or IC operation is interrupted directly. The operation of the current IC temperature sensing circuit is mainly implemented by an internal current source and an analog/digital converter inside the IC. As the forward voltage drop in a semiconductor PN junction varies proportionally with the temperature, the IC temperature sensing circuit could use such characteristic to detect the temperature of the IC. However, almost all the current temperature sensing circuit needs an operational amplifier and a band-gap voltage reference source. Thus, the current temperature sensing circuit cannot apply to a low-voltage IC environment. Further, the current temperature sensing circuit itself lacks an intrinsic temperature threshold control function. The temperature sensing function and the temperature threshold control function are separately realized with independent circuits, which are cascaded afterward. Therefore, the conventional technology not only inconveniences designers, but also increases the cost of manufacturing.
In order to solve the abovementioned problems, the present invention proposes a temperature sensing circuit for low voltage operation, which contains a temperature threshold control unit that can persistently send out an over-temperature alert until the temperature is lowered to a specified value, the present invention also lower the production cost since it does not require the use the operational amplifier and the band-gap voltage reference source.